KABUL — U.S. forces in Afghanistan saw their supply lines squeezed from the north and east Tuesday after militants blew up a bridge in Pakistan, and Kyrgyzstan said it would end U.S. use of a key air base following Russia's announcement of new aid for the Central Asian nation.

Securing efficient and safe supply routes into Afghanistan has become a top priority for U.S. officials as the Pentagon prepares to send in up to 30,000 more American forces this year. Some 75 percent of U.S. supplies travel through Pakistan, where militants have stepped up attacks on truck convoys destined for U.S. bases.

Attackers on Tuesday blew up a bridge in northwestern Pakistan in a fresh salvo in an escalating campaign to cripple Washington's war effort in Afghanistan.

The red metal bridge in the Khyber Pass partially twisted and collapsed on one end, with chunks of concrete scattered about. A trailer truck caught on the span — about 15 miles northwest of Peshawar — fell on its side and spilled dozens of bags.

Seeking supply routes
While U.S. officials have long said they are seeking fresh supply routes, they have never hinted publicly that they are concerned about running out of food or fuel. American forces stockpile enough supplies to last 60-90 days in the event that their supply chain is severed, U.S. officials say.

The top U.S. military spokesman in Afghanistan shrugged off any supply worries after Tuesday's events, saying that traffic was already flowing again in Pakistan after the attack. "They made a bypass," said Col. Greg Julian.

He also dismissed Kyrgyzstan's threat to close access to the Manas air base as nothing but "political positioning." Gen. David Petraeus, who oversees the wars in Afghanistan and Iraq, met with officials in Kyrgyzstan last month and "came away with the sense that everything was fine," Julian said.

"We have a standing contract, and they're making millions off our presence there. There are no plans to shut down access to it anytime soon," Julian told The Associated Press.

Pentagon spokesman Geoff Morrell said: "I have seen nothing to suggest, other than press reports, that the Russians are attempting to undermine our use of that facility."

Petraeus, chief of the U.S. military's Central Command, said last month that agreements had been reached to use supply routes through Central Asia, but details of the deals have not been announced.

President Kurmanbek Bakiyev's statement that U.S. forces would have to stop using Manas air base came after Russia said it was providing the poor Central Asian nation with billions of dollars of aid.

The Kyrgyz government "has made the decision on ending the term for the American base on the territory of Kyrgyzstan and this decision will be announced tomorrow or the day after," Bakiyev said in televised comments.

The United States set up the Manas base and one in neighboring Uzbekistan to back operations in Afghanistan after the September 2001 terrorist attacks. Uzbekistan expelled U.S. troops from the base on its territory in 2005 in a dispute over human rights issues, leaving Manas as the only U.S. military facility in the region.

There are frequent U.S. flights between Manas and the main U.S. base in Afghanistan at Bagram.

Russia offers loan
Russia has long been suspicious of the U.S. presence. Russia also uses a military air base in the former Soviet nation.

Afghan President Hamid Karzai has made increasing overtures to Russia in recent weeks. His office released correspondence between the two countries saying Russia is ready to cooperate on defense matters.

During his visit last month, Petraeus said that Manas would be key to plans to boost the U.S. troop presence in Afghanistan. He also said the United States pumps $150 million into Kyrgyzstan's economy annually, including $63 million in rent for Manas.

Russia agreed Tuesday to provide Kyrgyzstan with $2 billion in loans plus another $150 million in financial aid.

Central Asia is key to U.S. efforts to secure an alternative supply line to forces in Afghanistan. The main route, through the Khyber Pass in Pakistan's northwest, has occasionally been closed in recent months due to rising attacks by bandits and Islamist militants.

Pakistan's government has dispatched paramilitary forces to escort supply convoys and sought to crack down on militants in the Khyber zone, but attacks have persisted in an area that had been largely free of violence until three years ago.

The U.S. and NATO fly ammunition, weapons and other sensitive supplies into Afghanistan, but it would be too costly to ship everything that way.

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